Telescopic load booster

ABSTRACT

A HYDRAULICALLY OPERATED, TELECOPIC FORKLIFT HAVING A MANIFOLD IN THE HYDRAULIC CIRCUIT INTERCONNECTING THE PUMP, THE CYLINDER FOR ACTUATING THE LIFT CARRIAGE AND THE CYLINDER FOR ACTUATING THE TELESCOPIC MAST. THE MANIFOLD INCLUDES A FLOW-RESTRICTING ORIFICE LEADING TO THE MAST CYLINDER AND THIS ORIFICE ESTABLISHES A PRESSURE DIFFERENTIAL BETWEEN THE PRESSURES AT WHICH THE TWO CYLINDERS ARE ACTUATED THEREBY ACHIEVING A CONTROLLED SEQUENTIAL OPERATION BOTH IN LIFTING AND LOWERING A LOAD.

United States Patent 2,518,251 8/1950 Quayle ln ventor Raymond Carl Tait Cleveland, Ohio Appl. No. 762,678 Filed Sept. 26, 1968 Patented June 28, 1971 Assignee Hunter Manufacturing Company Cleveland, Ohio TELESCOPIC LOAD BOOSTER 6 Claims, 3 Drawing Figs.

[1.8. CI 187/9, 91/41 1 Int. Cl B661 9/22 Field of Search 187/9, 17; 91/41 1, 412

References Cited UNfl ED STATES PATENTS 2,598,233 5/1952 Deardorfl" 91/412 2,821,264 1/1958 Ulinski 187/9 3,135,283 6/1964 Keel 91/412(X) 3,208,556 9/1965 Shaffer..... 187/9 3,276,549 10/1966 Ramsey 187/9 Primary Examiner-Milton Buchler 1 Assistant Exam iner-- Jam es E. Pitten'ger Attorney- Yount & Tarolli ABSTRACT: A hydraulically operated, telescopic forklift having a manifold in the hydraulic circuit interconnecting the pump, the cylinder for actuating the lift carriage and the cylinder for actuating the telescopic mast. The manifold includes a flow-restricting orifice leading to the mast cylinder and this-0rifice establishes a pressure differential between the pressures at which the two cylinders are actuated thereby achieving a controlled sequential operation both in lifting and lowering a load.

PATENTED JUH28 IBYl INVIENTOR. RAYMOND CARL TAIT zfl wffior ATTORNEYS.

TELESCOPIC LOAD BOOSTER This invention relates to the art of work and material-handling equipment and more particularly to load boosters such as forklifts and the like.

Although the invention will be described with particular reference to forklifts, it is to be understood that the invention has broader application and may be employed with any loadlifting apparatus which employs a telescopic mast or track along which the load-supporting means travels as the load is lifted.

It is conventional practice to construct forklifts with a roller-mounted carriage to which the forks or other load-supporting means are attached. A vertical mast or track is mounted on the frame of'the lift with the mast being ofa twopiece construction, a stationary portion and a vertically movably portion which is adapted to be extended above the stationary portion to increase the vertical distance over which the load may be lifted. The carriage is adapted to travel along appropriate tracks or guideways within the vertically movable portion of the mast. Typically, the prior art forklifts have employed a pair of hydraulic cylinders, one of which is adapted to actuate the carriage to move it over a vertical distance while the other cylinder is adapted to actuate the movably portion of the mast to extend it above the stationary portion of the mast.

From the standpoint of simplicity of operation and economy of construction, it is highly desirable that relatively low hydraulic pressures, that is 2,000 psi. or lower, be employed in the hydraulic systems of forklifts. This is particularly so with the smaller sizes of forklifts, such as those having a lifting capacity of2,000 pounds or less. Accordingly, it has been conventional to employ single-acting cylinders and a single pump to supply the fluid under pressure to both cylinders. However, it is necessary with construction of this type to provide for a certain amount of free lift of the carriage before the movable portion of the mast is extended. Thus, the carriage must be capable of traversing the lowered height of the mast before the movable portion of the mast is extended and this requires the cylinder actuating the carriage to be activated before the cylinder controlling extension of the mast is actuated. The prior art has accomplished this by employing a mechanical latch which has latchedthe movable portion of the mast to the fixed portion of the mast. In this manner, the pressurized fluid delivered by the pump initially is effective only to actuate the carriage for movement vertically along the mast and is ineffective to extend the movably portion of the mast. As the carriage reaches the top of the fixed portion of the mast, it trips the latch and thereby enables the pressurized fluid to be effective to actuate the cylinder to raise the movable portion of the mast.

Although this arrangement has proven to be generally satisfactory, certain shortcomings have been experienced. Chief among these is the tendency of the load to drift downward at a rate which cannot be controlled by the operator. This drift condition is most noticeable when the load is being lowered with the mast extended. Thus, assuming the load is in an elevated position with the mast extended and it is desired to lower the load, the operator will actuate a valve which will relieve some of the hydraulic pressure in the system to permit the load to descend under the force of gravity. However, since there is but a single hydraulic circuit for both the cylinder which controls the position of the mast and the cylinder which controls the position of the carriage, it has been found that the mast may descend at one rate and, simultaneously, the carriage may descend at a different rate with the result that it is extremely difficult to gauge the rate of descent on the load. Moreover, even after the valve has been closed, there is often a tendency for either the carriage or the mast to drift downward for a period of time until the hydraulic pressures in the two cylinders have stabilized.

The present invention contemplates a new and improved hydraulic control system for forklifts which overcomes all of the above-described problems. as well as others, but which is extremely simple in construction and economical to manufacture.

it is the primary object of this invention to provide a hydraulic system for forklifts of the type described above in which precise control of the position of the mast and the carriage is obtainable at all times and the undesirable drift condition heretofore experienced is eliminated.

in accordance with the present invention, there is provided a forklift having a carriage moveable along a telescopic mast with a first cylinder for controlling the movement of the carriage and a second cylinder for controlling the extension of the mast. A single pump supplies hydraulic fluid under pressure to the two cylinders through a manifold means incorporated in the circuit. The inlet of the manifold is connected to the pump. The manifold includes two outlet ports, one of which is connected to the cylinder for actuating the mast and the other of which is connected to the cylinder for actuating the carriage. One of the outlet ports is of a size that the hydraulic fluid may readily flow therethrough while the other of the outlet ports is substantially smaller in size and comprises a restrictive orifice. This manifold arrangement, coupled with the dif ferential weights which the two cylinders must lift, eliminates the necessity for a releasable latch between the fixed and moveably portions of the mast and also eliminates any tendency of the load to descend at an uncontrolled rate or to drift downwardly. Moreover, this arrangement provides a controlled sequence of operation in which the mast always descends before the carriage.

The invention described herein may take physical form in certain parts and arrangements of parts, a preferred embodiment of which will be described in detail herein and illustrated in the accompanying drawings which form a part hereof.

Referring now to the drawings wherein like reference numerals indicate like parts in the various views:

FIG. 1 is a perspective view ofa typical forklift in which the invention may be employed.

FIG. 2 is an elevation view, partly in section of a typical hydraulic cylinder and manifold which may be used with the forklift of FIG. 1.

FIG. 3 is a schematic hydraulic circuit diagram which employs the principles of this invention.

Referring now to the drawings, wherein the showings are for the purposes of illustrating the preferred embodiment of the invention only and not for the purposes oflimiting same, FIG. 1 illustrates a load booster or forklift indicated generally be the reference numeral A. The forklift is generally of a conventional construction and employs a base or frame B supported by rollers or casters enabling the lift to be moved to the desired location. It will be appreciated that the lift may be either manually operated or power operated. The lift further includes a mast, indicated generally by the reference numeral C, and a carriage and load supporting means, generally indicated by the reference numeral D. These basic components comprise the conventional forklift and it is this specific environment in which the invention has particular application.

Referring now in more detail to the construction of the forklift, the mast C is of a two part-construction and employs a fixed mast portion 10 and an extensible or telescopic mast portion 11. The mast portion 11 is mounted by any appropriate conventional means for movement within and along the length of the fixed mast portion 10 so that the portion 11 may be telescopically extended above the mast portion 10 in the manner shown in FIG. 1. The carriage D comprises a carriage frame generally indicated by the reference numeral 15 and includes rollers (not shown) which cooperate in conventional fashion with a track or guideway formed in or carried on the movable mast portion 11. A pair of forks 16 or other loadsupporting means may be supported on the carriage frame 15. it will be appreciated that the forks 16 are merely exemplary of one form of load-carrying means and other load-supporting means such as a drum handler or various other types of equipment, all of which are conventional in the art, may be used in lieu of or in conjunction with the forks.

To actuate the carriage D there is provided a first hydraulic cylinder 20, one end of which is supported on a base member 22 connected to the lower end of the movable mast 11. The

cylinder includes an extensible piston rod 24, the upper end 26 of which is connected by any appropriate means to the carriage frame 15, such that as the piston rod 24 is extended, the carriage is moved on its rollers vertically along the guideways within the movable mast l 1.

There is also provided a second cylinder 30. This cylinder, like the first cylinder 20, is positioned in a vertical position with the lower end'of the cylinder being mounted on the base frame 32 of the lift. The cylinder 30 also includes an extensible piston rod 34, the upper end 36 of which is connected by any appropriate means to the movably mast l1 and is effective, when actuated, to extend the mast portion 11 above the mast portion 10.

Both of the cylinders 20 and 30 are single-acting cylinders and'may be of the type generally shown in FIG. 2. As shown in the HQ, the cylinder 30 employs a conventional packing 38 which surrounds the extensible piston rod 34 and a packing nut 39 which may be employed to adjust the compression of the packing. In this connection, it is to be noted that the adjustment of the packing nut and the consequent compression of the packing material 38 will have an effect on the move ment of the piston rod 34, in that the greater the compression on the packing 38, the greater the frictional drag that will be imposed on the piston rod.

The cylinder 30 further includes a piston 40 which is connected to the inner end of the piston rod 34 and cooperates with the inner walls of the cylinder to define a fluid chamber 42 in conventional manner. An inlet port 44 is formed in the wall of the cylinder 30 and permits the introduction of fluid pressure into the chamber 42.

The above description of the cylinder 30 also applies to the cylinder 20 which is of an identical construction and size. However, it is contemplated that, in addition to this conventional construction of the cylinders 20, 30, there will be included with the cylinder 30 a manifold, indicated generally by the reference numeral 50.

The manifold 50 includes an inlet port 52 and outlet ports 54, 46. The outlet port 56 is aligned with the inlet port 44 for the cylinder 30 while the outlet port 54 is connected through appropriate fluid lines to the corresponding inlet port of the cylinder 20. Port 52 is connected to the pump 60.

Referring now to H6. 3, there is a schematic illustration of a typical hydraulic circuit employing the manifold 50 and the cylinders 20, 30. Thus, a motor 61 is coupled to the pump 60 and drives the pump to supply fluid under pressure from the tank or reservoir 62. The pump 60 is connected to the manifold 50 by the fluid line 63. A conventional solenoidoperated check valve 64 is inserted in the line 63. A relief valve 65 may be positioned in the line 63 between the pump and the check valve and a second relief valve 66 may be positioned between the manifold 50 and the check valve 64. A fluid line 68 connects the manifold 50 to the cylinder 20.

Referring now in more detail to the manifold 50, it will be noted that the inlet port 52 and the outlet port 54 are of substantial size and may be of the same dimensions. Contrasted with these two ports is the outlet port 56 which is severely restricted in diameter as compared to the outlet port 54 and forms, in effect, a restrictive orifice through which the fluid must flow if it is to enter the fluid chamber 42 in the cylinder 30. The relationship between the port 54 and the restrictive orifice 56 is important to the operation of this invention. Although the precise dimensional relationship may vary, in substance, the port 56 must be sufficiently restricted in size that fluid under pressure introduced through the port 52 into the manifold 50 will follow the line ofleast resistance and flow outwardly through the port 54 rather than through the restrictive orifice 56. In this manner, the orifice 56 functions much as a valve in that the fluid, at least initially, is channeled through the port 54 to the cylinder associated with that port.

Coupled with this arrangement of ports in the manifold 50, is the different conditions under which the two cylinders 30 and 20 must operate. Thus, to lift a load supported on the forks 16, the cylinder 20 must raise the weight of the carriage B, the weight of the forks 16, the weight of the load supported on the forks and also overcome the friction inherent in the system. On the other hand, the cylinder 30 must lift, in addition to the foregoing, the weight of the movably mast 11 and also overcome the friction inherent in the sliding engagement of the two mast portions 10, 11 and must, therefore, lift a greater weight than the cylinder 20. This differential in weight, which is inherent in the construction of the system, coupled with the differential port sizes in the manifold 50, cooperate to achieve the desired result.

Thus, assuming the forklift of FIG. 1 is in its inoperative position with the movable mast 11 and the forks l6 lowered and a load resting on the forks 16 waiting to be lifted, the operator will then actuate the motor 61 to drive the pump 60 which will introduce fluid under pressure through the check valve 64 into the manifold 50. The fluid entering the manifold 50 through the port 52 will be confronted with the relatively restricted orifice 56 and the open outlet 54, and, following the path of least resistance, will tend to flow into the fluid chamber of the cylinder 20. As a result, the fluid will accumulate in the cylinder 20 and establish a pressure which will cause the piston rod 24 to extend upwardly carrying with it the carriage D and the load supported on the forks 16. Although the pressure developed in the system to extend the piston rod 24 upwardly may cause some of the fluid to pass through the restrictive orifice 56 into the chamber of the cylinder 30, the differential in weight described above prevents the piston 30 from being actuated. For example, assuming a load of 2,000 pounds resting on the forks 16 and further assuming that a pressure of 1,7000 p.s.i. is required to actuate the cylinder 20 to lift that load, the additional weight which the cylinder 30 must lift will require a pressure in excess of that value. As a result, any fluid which may tend to bleed through the orifice 56 into the chamber of the cylinder 30 will be at a pressure which is insufficient to actuate the cylinder 30. At any point during this free-lift portion of the carriage movement, the pump may be discontinued and the system will be hydraulically locked, supporting the load in its elevated position. However, if it is desired to lift the load beyond the free-lift distance, it is necessary to extend the movable mast 11. This is accomplished by extending the piston 24 to its fullest extent at which point the carriage frame 15 engages a top stop supported on the mast thereby preventing any further upward movement of the carriage. However, the pump 60 continues to deliver fluid into the system and the pressure thus builds up in the cylinder 20 and in the system until it has achieved a level at which the flow rate of the fluid through the restrictive orifice 56 into the cylinder 30 is sufficient to build up a pressure in the cylinder sufficient to actuate the cylinder and commence to extend the piston rod 32 and the mast portion 11 to which it is connected. As the mast 11 moves upwardly, it carries with it the cylinder 20, carriage D and the load positioned on the fork 16. When the load has been lifted to the desired height, the pump is discontinued and the system is hydraulically locked thereby maintaining the load in its elevated positron.

Assuming it is then desired to lower the load a predetermined amount, the operator need only actuate the valve 64 to dump a portion of the fluid back to tank. It has been found that when this occurs, the piston rod 24 will remain in its fully extended position, thus maintaining the carriage in a fixed position relative to the movable mast 11. However, fluid in the cylinder 30 will pass outward through the restrictive orifice 56 into the manifold 50 and back to tank thereby causing the movable mast 11 to descend carrying with it the carriage and load as described above. Should the valve be maintained in its open position, the movable mast 11 will fully descend to its lowered position before the carriage and load will commence to descend relative to the mast. Contrasted with this operation is that of the prior art which did not employ a manifold having the differential ports described herein. With the prior art construction and with the movable mast extended, any opening of the valve to dump a portion of the fluid back to tank would result in both the carriage and the mast l1 descending, often times at differential rates which were extremely difficult to gauge. Moreover, should the valve subsequently be closed with the mast partially extended, it frequently occurred that a period of time would be required for the two cylinders to reach equilibrium and the system to stabilize. As pointed out above, this undesirable result is obviated by the present construction which assures a controlled sequential operation. 1

The precision dimensional relationships between the port 54 and the restricted orifice 56 may vary. In one satisfactory arrangement, the port 54 has been nine-sixteenths inch in diameter while theres'tricted orifice 56 has been threesixteenths inch in diameter. With that relationship, a pressure differential of l00 p.s.i. has been required to actuate the cylinder 30. Thus, assuming a pressure of 1700 p.s.i. is required to actuate the cylinder 20, a pressure of 1800 p.s.i. has been required before the cylinder 30 will be actuated. Obviously, other sizes of ports and orifices and other pressure differentials may be employed, since there are many variables which may affect the operation of the system in any given forklift. For example, the friction inherent in the system may vary depending on the mounting of the movable mast within the fixed mast and also the mounting of the carriage within the movable mast. In addition, it is possible to vary the frictional engagement between the packing and the piston rod of each of the cylinders 20, 30 simply by adjusting the gland nut 39. By so doing, the frictional resistance which the piston rod 34, for example, must overcome may be increased thus necessitating a higher pressure level before the cylinder 30 will be actuated.

As pointed out above, it is highly desirable to maintain the pressure in the system at a level below 2000 p.s.i. Should the pressure exceed that level, more expensive fittings would have to be employed in the fluid system. Accordingly, the size of the restrictive orifice 56 must be such that the pressure built up in the system does not exceed 2000 p.s.i. before the pressure is effective to actuate the cylinder 30. It has been found that if the orifice is too small, the back pressure created in the system by the orifice 56 becomes excessive and the system pressure will exceed 2000 p.s.i. On the other hand, if the restrictive orifice is too large, the back pressure becomes less but the proper operation of the system is unduly sensitive to the proper balancing of the frictional forces in the system. For example, it has been found that if the back pressure built up before the cylinder 30 is actuated is 50 p.s.i., proper operation of the system does require some adjusting of the frictional forces including the gland nuts on the cylinders. However, if the pressure differential is maintained in the vicinity of l00 p.s.i., the sensitivity to frictional forces is substantially reduced and satisfactory operation is achieved.

The invention has been described with reference to but a single preferred embodiment. Modifications and alterations in this embodiment will occur to those having ordinary skill in the art and it is intended that such modifications and alterations are to be included within the scope of the invention as defined by the appended claims.

I claim:

1. In a load-supporting mechanism having a load-lifting means and telescoping track means for said load-lifting means, said load-lifting means including work-supporting means and first hydraulic cylinder means for moving said work-supporting means between first and second positions along said track means, said telescoping track means including second hydrauc linder is actuated; sal flow-restricting means comprising manifold means in said system; said manifold means having an inlet connected to said an outlet in said manifold means in communication with said first cylinder; and

a restrictive orifice in said manifold means in communication with said second cylinder;

said restrictive orifice being substantially smaller in size than said outlet.

2. The improvement of claim 1 wherein said pressure differential is approximately p.s.i.

3. In a load-lifting mechanism having load-lifting means and track means for said load-lifting means, said load-lifting means including a carriage movable along said track means, said track means including a fixed portion and a movable portion, first hydraulic cylinder means for moving said carriage along said track means, second hydraulic cylinder means for moving said movable portion of said track means and a hydraulic system including a single pump and fluid conduits interconnecting said first and second cylinders with said pump whereby fluid under pressure may be delivered to said cylinders, the improvement comprising:

manifold means in said system;

said manifold means having an inlet port connected to said pump and first and second outlet ports connected to said first and second cylinders, respectively;

said second outlet port being substantially smaller in size than said first outlet port and forming a restrictive orifice through which fluid must pass when said second cylinder is actuated.

4. The improvement of claim 3 wherein said second cylinder is operative when actuated to move both said movable track portion and said carriage.

5. The improvement of claim 4 wherein said first cylinder is supported on said movable track portion.

6. The improvement of claim 3 wherein the dimensional relationships of said outlet ports is such that a pressure differential of approximately I00 p.s.i. is established between the pressure at which said first cylinder is actuated and the pressure at which said second cylinder is actuated. 

